1. Field of the Invention
The present invention relates generally to dust caps that engage with fiber optic connector adapters and, more particularly, to dust caps that have a structure operable for securely engaging the internal geometry of a fiber optic connector adapter, and optionally including material that reacts with invisible light emanating from a connector engaged with the back side of the adapter to produce a visual signal.
2. Technical Background
Fiber optic applications using optical connectors and adapters frequently include requirements for the identification of specific optical fibers during installation, interconnection and maintenance testing. Examples of such applications include multi-dwelling units, cabinets, local area networks and industrial networks, among others. Within these systems, connections between optical fibers are typically accomplished through the use of adapters mounted within patch panels, cabinets or racks. A patch panel typically includes a large number of optical connectors pre-installed into the backside of a number of connector adapters, thus providing partially populated adapters. The front side of the adapters are typically covered until needed using some form of covering to prevent dust and other contamination from entering the adapter and contacting the polished end face of the back side connector.
When a specific connector of a panel is needed for interconnection with another connector, visible light, commonly a red laser diode source from a Visual Fault Locator (VFL), is used to perform optical fiber tracing for connector identification. Visible light introduced through the back side connector is typically visible through the front side of an unpopulated adapter, and in the case of an adapter covered with a dust cap, the dust cap is typically translucent such that the visible light is detectable through the dust cap. In the case of invisible light being transmitted through the back side connector, the visible light requires detection through the use of costly detection equipment only after the dust cap has been removed from the adapter. When removing a dust cap to detect the invisible light, the opportunity exists for eye damage if the light is accidentally viewed. Further, removing the back side connector from its adapter or removing the dust cap from the front side of the adapter also introduces an opportunity for dust and other contamination to reach the polished end face of the back side connector that may damage or degrade a signal.
As stated above, dust caps are typically made from opaque plastic materials, such as low-density polyethylene materials. Dust caps have also been designed to engage adapters by interference fit, and have not included structure to engage with the adapter in the manner that a connector does, thus conventional dust caps have failed to provide proper long-term engagement, and as a result, commonly disengage from their adapter and fall to the floor. One example of a conventional, translucent dust cap that mounts by interference fit is shown in FIG. 1. Generally, the dust cap 10 includes a cylindrical sleeve 12 having an open first end 14 and an opposed second end 16 that is closed by a translucent end member 20. The sleeve 12 further defines a partially lengthwise extending bore 18 for receiving a ferrule therein. The translucent end member 20 may be provided with a lens 22 to facilitate optical communication. Further, the lens may be provided with an opaque portion to block light transmitted directly along the optical axis to prevent eye damage. A medial portion of the sleeve 12 defines an internal chamfer 24 to interfere with ferrule structure. As visible light from a ferrule emanates through the lens 22 it is detectable.
While conventional dust caps are suitable for detecting visible light through the dust cap, by design they are not capable of detecting invisible light through themselves, and are not properly designed to remain engaged for long periods of time without becoming dislodged. Disadvantageously, a long term interference fit requires tight molding tolerances of both the dust caps and the adapters. Further, conventional dust caps are subject to thermal expansion and other external forces such as vibration which may cause the dust cap to dislodge from the adapter.
Accordingly, what is desired is an adapter dust cap that not only protects against dust contamination, but also engages the internal structural geometry of the adapter to ensure a secure fit that is resistant to vibration and other forces such as thermal expansion. Additionally, it would be desirable for the adapter dust cap to provide a visual indication of either visible or invisible light transmitted through a back side populated adapter for connector identification. It would further be desirable for the dust cap to diffuse visible and/or invisible light of sufficient power to cause eye damage if viewed along the optical axis.